Although I am not intimately familiar with the adsorption process that activated carbon exhibits, I can get some rough numbers looking at this from a chemistry point of view so long as I make a number of inaccurate assumptions.  First off, the surface area of a gram of activated carbon can vary greatly depending on the method of manufacture, however one published value I have pegs it at 10,000 sq ft / gram⁽¹⁾ Now, let's assume that it has the ability to adsorb these gold particles with 100% efficiency (not a reasonable assumption).  Second, the atomic radius of the gold +1 ion is approximately 151 pm⁽²⁾.  Because this is not going to arrange itself in the normal crystal structure of gold (since it is just the ion) we will make things easier by assuming some sort of primitive arrangement (like a grid of gold atoms).  With all of these assumptions in place we are basically determining how much a sheet of gold ions would weigh that would cover 10,000 square feet, or a area 100 feet by 100 feet.

So, how many gold ions, side by side would it take to stretch 100 feet? 

151 pm = 1.51 x 10^-10 meters

We have a square with this many atoms on each edge.  So, figure out how many atoms in the square by determining the area, then divide by Avogadro's number to get the mols.  Finally multiply by molecular weight to get the amount of gold that could be adsorbed.

(191698113207 atoms)² = 36748166607333570665717 atoms / 6.022141 x 10²³ atoms/mol= 0.610 mol
0.610 mol x 196.96 g/mol = 12.0188 g gold / gram carbon

Now, that's a lot of gold to be adsorbed by 1 gram of activated carbon.  Thankfully I have actual numbers from other sources.  And this was just me messing around to no real end.  In an article titled "The Carbon-In-Pulp Process" by Stephen Hill(3) the author examines using activated carbon to recover gold and silver from cyanide leach solutions.  There are two interesting in the article.  First was the Carlton Mill in Cripple Creek, CO.  In that example gold was extracted using activated carbon until the carbon had reached a saturation of 40 tr oz/st.  The second section of the article giving an overview of the process states:

"Frequent stripping and handling can result in lower loading, so most large operations usually load the carbon to 200 to 400 tr oz/st Au before the carbon is removed from the first tank in the cascade."⁽³⁾

400 tr oz/st corresponding to 0.0137 grams of gold per gram of carbon (At least this is an industrial example).  Meaning my calculation above is 1000 times off.  But there are a number of factors that can cause this to vary, this is an equilibrium process, concentration of other cations and anions in the solution, mixing, circulation, identity of other constituents in the system, contact time, etc. 

C.W. Ammen's book on the precious metals says nothing about the amount of material recoverable by this method, just that it occurs.  Although I can't give any of the hard fast numbers I want to give, the above can act as a guide, meaning that if you want to reliably collect 10 grams of gold from your solution, then you will need to treat it with 730 grams of activated carbon.  Finally though, a general internet search reveals that:

"The minimum load of carbon rule of thumb is one pound of activated carbon per 0.1 ounce of gold present in the solution. Usually, it is several pounds per 1/10 ounce, though, as the cost of carbon is relatively insignificant compared to timely recovery of gold."⁽⁴⁾

Converting this so it matches the previous value you get 3.11 g (If you're using troy ounces) per 454 grams carbon or  0.0068 grams of gold per gram of carbon which is an even lower value.  So, here  I present to you some values to consider.  Again, remember, this will vary depending on conditions but hopefully this will give you some direction.

 

References:

(1) Lewis, J. Richard Sr.  Hawley's Condensed Chemical Dictionary. 13th ed. Wiley, USA 1997

(2)"Gold." Gold Elemental Facts. Chemicool. 1 Feb. 2009 <http://www.chemicool.com/elements/gold.html>.

(3) Hill, D. Stephen. "The Carbon-In-Pulp Process." Bureau of Mines Information Circular 1986: 40-43.

(4) "Carbon Adsorption." Carbon Adsorption In Recovery Of Gold From Cyanide Leach Solutions. Mine-Engineer.com. 1 Feb. 2009 <http://www.mine-engineer.com/mining/minproc/carbon_ad.htm>.